Rules of Go

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This is an in-depth discussion of the rules of Go. While the basic idea of go, conveyed by the outline rules given first, is not particularly complex, there are some subtle but complex issues surrounding these rules. Such issues need not be studied when first learning to play —in fact many strong players do not fully understand them!— but they may be of interest to more experienced players.

Contents

[edit] Basic rules

[edit] Players

Rule: There are two players, called Black and White.

Go is a game between two players.

[edit] The equipment

[edit] The board

The board, or "goban"
The board, or "goban"

Rule: Go is played on a board. The board is a grid of 19 horizontal and 19 vertical lines.

Beginners might prefer to play on a small board with 9 horizontal and 9 vertical lines (9 × 9 board). On this board learning tactics is easier and one is not confused by the complex strategies seen on big boards.

A point on the grid where a horizontal line meets a vertical line is called an intersection.

There are 361 intersections on the regular 19 × 19 board. In the following diagram, the mark (red circle) indicates one of the 25 intersections of the small 5 × 5 board:

(To save space, most diagrams show small boards. Here we have a 5 × 5 board.)

[edit] Stones

Rule: There are black and white stones.

The player Black uses black stones, the player White uses white stones. The diagram shows some stones on some intersections of the board:

[edit] The state of stones on the board

[edit] Chain of connected stones

Definition: A chain consists of one stone or of several stones that are of the same colour and mutually connected via lines of the grid.

This is a chain of 6 black stones:

[edit] Liberty

Definition: A liberty of a chain is an empty intersection adjacent to it.

The marked intersections (red circles) are the liberties of the black chain:

It is possible to have liberties within (completely surrounded by) a group.

[edit] Removal

Rule: A play removes any stones or chains without liberties.

   
  
Before    Black plays    After removal

In most cases a play does not remove a chain. A play might remove a large chain of several stones. Removing an opponent's chain(s) is also called a capture.

[edit] Permanent Placement

Rule: "A stone laid is a stone played" -- all stones remain on the board until the game's end, unless captured by an opponent.

[edit] Play

[edit] Turn-based play

Rule: The players alternate. Black starts.

Before Black plays first, the board is empty. Black makes a first play on one of the intersections. Then White makes a second play somewhere:

   
  
Start    Black plays    White plays

The game will continue with Black and White alternating.

[edit] Play or pass

Rule: On his turn, a player may either place one stone on the board or pass.

Normally, a player having the turn makes a play. However if he does not think he can improve his position he may pass. This generally happens at the end of the game, when all territory has been claimed and further moves seem useless, or even harmful to a player's position. Alternation continues with his opponent.

Note: In some rulesets, a pass is accompanied by giving the opponent a stone as a 'capture' as part of 'passing'.

[edit] Empty intersection

Rule: When a player makes a play, he puts one stone of his or her colour on an empty intersection.

The following diagram shows how Black could make a play:

[edit] No suicide (not present in some variations)

Rule: You cannot place a stone where it would have no liberties (or be a part of a larger chain with no liberties), unless the play completes a removal of opposite stones.

For example, in the above diagram, black can't play at the circled point.

For example, in the above diagram, white can't play at the circled point.

Note: Some Go rulesets allow suicide of more than one stone.[verification needed] The chain with no liberties is removed from the board.


[edit] Ko (no repetition of the same shape)

Rule: If recapturing a stone would recreate the same board position from the previous move, the position is called ko, and the recapturing move is illegal.

In the position above, Black has just captured a stone at the circled point by playing to the right of that point. White could now recapture Black's stone, and so on in infinite stalemate. The ko rule prevents this situation and enables the game to keep moving. This "basic ko rule" is adequate for the simplest kind of ko, which occurs when two single stones could otherwise recapture each other indefinitely. This situation occurs in most games and often has a major or even decisive effect on the result. To prevent endless repetition, the rule of ko forbids plays that would repeat the previous board position. A player may not recapture on their next move and must play elsewhere (or pass). After a new move, the board position will be different, and the stone may then be recaptured.

Other positions which could lead to an endlessly repeating position are rare enough that many frequent players never encounter them; their treatment depends on what rule set is being used. Under some rule sets, such games may be considered "no result" (as if the game never happened). The AGA and New Zealand rule sets have a "superko" rule forbidding any move that repeats any previous board position. The Ing rules feature a complicated distinction between "fighting" and "disturbing" ko.

The word ko (Japanese: 劫 kō; usually written with katakana コウ) means "kalpa" in Japanese [1], and is pronounced with a double-length "o", making it sound somewhat like 'kou' does in English.

[edit] Seki

Rule: When adjacent groups of black and white are neither alive nor able to capture each other, the situation is called seki.

If either black or white were to play at the captured point, the other side would then capture their group by playing in its eye.

Terminology: An 'Eye' is one (or more) empty intersections entirely surrounded by a chain of stones of one colour.

This corollary to all rule sets applies to situations in which groups of black and white stones have mutually dependent life, although neither Black nor White is alive independently. In most rule sets, the vacant points in a seki are treated as neutral points for counting purposes.

[edit] End

Rule: Alternate play ends when a player makes a pass and then his/her opponent also passes.

[edit] Winner

The player with the higher score is the winner. Margin of victory does not matter; winning by one point is as good as winning by 100 points. Different scoring rules exist which in practice almost always determine the same winner, see Scoring section below. You choose a rule set before starting the game.

[edit] Optional rules

[edit] Compensation

To allow players of different skills to compete fairly, handicaps and komi are used. These are considered a part of the game and, unlike in many other games, they do not distort the nature of the game. Players at all levels employ handicaps to make the game more balanced.

[edit] Komi

Main article: Komidashi

In an "even", or non-handicap game, Black's initial advantage of moving first can be offset by komi (compensation points): a fixed number of points, agreed before the game, added to White's score at the end of the game. The correct value of komi (to properly compensate for Black's advantage) is controversial, but common values are 5.5, 6.5 or 7.5 -- the fractional value avoids a tied game. In a handicap game, komi is usually set to 0.5 (i.e. White wins if the game is tied). A handicap game with a handicap of 1 starts like an even game, but White receives only 0.5 komi (i.e. a White player who is stronger by one rank is handicapped only by Black's first-move advantage).

[edit] Handicap

Main article: Go handicaps

Handicaps are given by allowing the weaker player to take Black, and declaring White's first few moves as mandatory "pass" moves. In practice, this means that Black's first move is to place a set number of stones (usually the number is equal to the difference in the players' ranks) on the board before allowing White to play. Traditionally, the hoshi ("star points") -- strategically-important intersections marked with small dots -- are used to place these handicap stones. On the 19 × 19 board, there are nine star points: at the four 4-4 points in the corners, at the four 4-10 points along the sides, and one at the 10-10 point (the centre of the board, or tengen in Japanese). Smaller boards such as the 13 × 13 and 9 × 9 also have star points. The 13 × 13 has 9 at the 4-4 points, 4-7 points, and the center. The 9 × 9 board has only 5 points: the 3-3 points and the center.

When Black is only one rank weaker (also known as one stone weaker, due to the close relationship between ranks and the handicap system) he or she is given the advantage of playing Black, perhaps without komi, but without any mandatory White passes. For rank differences from two through nine stones, the appropriate number of handicap stones is used. Beyond nine stones, the difference in strength between the players is usually considered great enough that the game is more a lesson, with White teaching Black, so nine stones is the nominal upper limit on handicap stones regardless of the difference in rank (though higher numbers of stones, up to 41 stones in some cases, can be given if the teacher wants more of a challenge).

[edit] Thinking times

See the Time control section of the main Go article.

[edit] Variations

Go was already an ancient game before its rules were codified, and therefore, although the basic rules and strategy are universal, there are regional variations in some aspects of the rules.

[edit] Scoring

The most prominent difference between rulesets is the scoring method. There are two main scoring systems: territory scoring (the traditional Japanese method) and stone or area scoring (the Chinese method). Care should be taken to distinguish between scoring systems and counting methods. Only two scoring systems are in wide use, but there are two ways of counting using "area" scoring.

[edit] Territory scoring (Japanese traditional method)

In territory scoring (Japanese traditional method), a player's score is determined by the number of empty locations that player has surrounded minus the number of stones their opponent has captured.

Typically, counting is done by having each player place the prisoners they have taken into the opponent's territory and rearranging the remaining territory into easy-to-count shapes.

[edit] Stone or area scoring (Chinese traditional method)

In stone or area scoring (Chinese traditional method), a player's score is determined by the number of stones that player has on the board plus the empty area surrounded by that player's stones.

There are several common ways in which to count the score (all these ways will always result in the same winner):

  • The oldest counting method is as follows: At the end of the game, all white stones are removed from the board, and the players use black stones to fill the entirety of the black territory. Score is determined by counting the black stones. Since the board contains 361 intersections, black must have 181 or more stones to win. This method is still widely used in mainland of China.
  • Around 1975, Taiwanese player and industrialist Ing Chang-ki invented a method of counting now known as Ing counting. Each player begins the game with exactly 180 stones (Mr. Ing also invented special stone containers that count each player's stones). At the end, all stones are placed on the board. One vacant intersection will remain, appearing in the winner's area; the number of stones of one color in the other color's area will indicate the margin of victory.

[edit] Attempts at reconciling the two scoring systems

If the game ends with both players having passed the same number of times, then the score will be identical no matter which method is used. AGA rules call for a player to give the opponent a stone when passing. This "passing stone" ensures a correct result under any counting method.

The tradition of agreeing upon certain outcomes without playing them out is notably more complicated under Japanese-style rule sets where stones are removed and territory counted (or not) even though such an outcome could not be reached under normal play.

[edit] Repetition

The major division in rules to prevent repetition is between the simple ko rule and the super ko rule: the simple ko rule (typically part of the Japanese ruleset) prevents repetition of the last previous board; while the super ko rule (typically part of Chinese derived rulesets) prevents repetition of any previous board. The super ko rule is further differentiated into situational super ko (includes whose turn it is) and positional super ko (ignores whose turn it is). The simple ko rule generally requires the inclusion of additional rules to handle other undesirable repetitions (e.g. long cycles which can lead to no result where the game must be replayed).

[edit] Suicide

Currently most major rule sets forbid playing such that a play results in that player's own stones being removed from the board, however some rule sets (notably, New Zealand derived rules and Ing rules) allow suicide of more than one stone. This hardly ever occurs in real games, but in certain circumstances a suicidal move may threaten the opponent's eye shape, yielding a ko threat.

[edit] Compensation

The major rulesets differ in how handicap stones are placed on the board: free placement (Chinese), where stones can be placed anywhere (as if the player's turn repeated); and fixed placement(Japanese), where tradition dictates the stone placement (according to the handicap). Area scoring rules and territory scoring rules also differ in the compensation given for each handicap stone (since each handicap stone would count under area scoring). Komi (compensation for going first) also varies, ranging from several fixed values (commonly 5.5, 6.5, or 7.5) to various meta-games to determine a value (notably Auction Komi).

[edit] Board sizes

Most Go is played on a 19 × 19 board, but 13 × 13 and 9 × 9 are also popular sizes. Historically other board sizes were commonly used (notably 17 × 17, a predecessor of the 19 × 19 board in ancient China). Go is also sometimes played on various novelty sized boards as small as 5 × 5 and larger than 19 × 19. All board sizes have an odd number of lines to ensure that there is a center point, possibly to make mirror go a less attractive strategy. Generally all rules apply to all board sizes, with the exception of handicaps and compensation (whose placement and values vary according to board size).

[edit] Issues

In general, there are three closely related issues which have to be addressed by each variation of the rules.

First, how to ensure that the game comes to an end. Players must be able to settle unsettled situations rather than going around in circles. And neither player should be able to drag the game out indefinitely either to avoid losing or to irritate the other player. Possible methods include: the super-ko rule, time control, or placing an upper bound on the number of moves. This is also affected by the scoring method used since territory scoring penalizes extended play after the boundaries of the territories have been settled.

Second, how to decide which player won the game; and should draws (jigo) be allowed. Possible terms to include in the score are: komi, prisoners captured during the game, stones in dead groups on the the board at the end of the game, points of territory controlled by a player but not occupied by his stones, his living stones, the number of passes, and the number of disjoint living groups on the board.

Third, how to determine whether a group of stones is alive or dead at the end of the game, and whether protective plays are necessary e.g. connecting a group which would be in atari if all dame were filled. If the players are unable to agree, some rules provide for arbitration using virtual attempts to capture the group. Others allow play to resume until the group is captured or clearly immortal.

[edit] Rule sets

There are many official rule sets for playing Go. These vary in significant ways, such as the method used to count the final score, and in very small ways, such as whether the two kinds of "bent four in the corner" positions result in removal of the dead stones automatically at the end of the game or whether the position must be played out, and whether the players must start the game with a fixed number of stones or with an unbounded number.

Rule sets include Japanese, Chinese, AGA (American Go Association), Ing, and New Zealand.

Further detailed information may be found at the following external links.

[edit] Japanese rules

These are rules used in Japan and Korea, and are in wide use throughout the West, sometimes known as "territory" rules. The scoring is based on territory and captured stones. At the end of the game, prisoners are placed in the opponent's territory and players rearrange the board so that territories are easy to count, leaving a visual image resembling the game, which some players find aesthetically pleasing. There is no superko (the triple ko leads to an undecided game.) Suicide is always forbidden. Komi is 6.5.

[edit] Chinese rules

This is the other major set of rules in widespread use, also known as "area" rules. At the end, one player (usually Black) fills in all of his/her captured territory, and the other (White) stones are removed from the board. Prisoners do not count. Black stones are then arranged in groups of ten -- eighteen such groups, plus half the komi, plus at least one additional stone = victory for Black. So for example with a komidashi of 7.5 points, under Chinese rules Black needs at least 185 stones on the board at the end to win. Komidashi is usually 7.5 points.

[edit] AGA rules

These are used by the American Go Association. Some special rules (like giving the opponent a prisoner when passing) are added, which make the area scoring and territory scoring equal.

[edit] Ing rules

The scoring is basically the same as area scoring, but is done with a special technique involving "Ing bowls". Both players must start with exactly 180 stones; the Ing Foundation makes special bowls that allow players to count their stones easily. Prisoners come back to the owner. After the game finishes, both players fill their empty territory with their stones. The one that gets rid of all of them is the winner. White pays Black eight points (komi) by placing four white stones in Black's territory at the beginning of the counting phase. As Black wins ties it is 7.5 in effect. The ko rule makes a distinction between "fighting" and "disturbing" ko. Multi-stone suicide is allowed. This ruleset was invented and promoted by Ing Chang-ki.

[edit] Differences

In most cases the differences between the rule sets are negligible. The choice of rule set rarely results in a difference in score of more than one point, and the strategy and tactics of the game are mostly unaffected by the rule set used.

[edit] See also

[edit] External links

Rules comparisons
Specific rule sets